This script will Cipher and Decipher to/from ROT13.
No external modules required. Script written for Python 3, no guarantees for Python 2 functionality.
Cipher:
python ROT13_Cipher_Decipher.py -c
Decipher:
python ROT13_Cipher_Decipher.py -d
Help:
python ROT13_Cipher_Decipher.py -h